That hose runs to the remains of the AI, you should replace it with another vacuum plug to completely eliminate the AI system. With the AI removed the silver AI attachments in the heads next to the spark plugs ought to be replaced by bolts and you should find four identical vacuum plugs on top, two on the carbs next to the manifold boot clamps and two on the manifolds again by the manifold boot clamps. Ideally the shop pulled the AI valve system from under the tank and removed all of the associated hoses and gave you all that stuff in a box.
